The overarching goal of this proposal is to explore the in vivo delivery pattern, and exposure of furosemide from furosemide tablets when given with water, milk, baby formula and Ensure Plus to healthy adult volunteers following an overnight fast, under conditions that are similar to dosing and feeding conditions in pediatric patients. Importantly, low solubility drugs are common in the pharmacopeia. Exploratory in vitro studies by the Center for Drug Evaluation and Research (CDER) have recently demonstrated that the solubility, and thus potentially the bioavailability, of poorly soluble drugs may be highly enhanced in the presence of liquids commonly used to dose medications in children, such as milk or baby formula. However, the effect of these dosing liquids on bioavailability of drugs needs validation in humans. Furosemide, which is Biopharmaceutics Classification System (BCS) class IV (low solubility, low permeability), is a model drug to determine if these in vitro results will translate to improved bioavailability. In addition to its status as a model drug, furosemide is a commonly used medication and the cornerstone of medical treatment for edematous conditions. Treatment failure due to poor bioavailability is thought to be common problem with furosemide. Thus, the characterization of effect of the dosing liquids on pharmacokinetic (PK) of furosemide molecule has substantial potential to impact human disease. In addition to the PK limitations of furosemide, there is a complex relationship between PK and pharmacodynamics (PD) with furosemide. Notably, due to threshold and ceiling portions of the dose response curve, positive changes in total bioavailability may not necessarily translate into improved drug efficacy if absorption is slowed and peak concentrations are reduced. As such, understanding the effect of changes in PK parameters on PD parameters will be critical in interpreting the results of the proposed PK study of furosemide. In the current application, we propose a randomized 4-way crossover normal subjects study of furosemide 20mg tablets with co-administration of water, milk, baby formula, or Ensure Plus. The study will involve a meticulous 36-hour inpatient biospecimen collection protocol in 8 normal volunteers and creation of a biorepository of the generated biospecimens. Furthermore, determination of furosemide concentrations in plasma and urine in addition to urinary sodium output (the PD response to loop diuretics), in-vitro solubility, dissolution, and protein binding experiments, followed by an integrated in vitro, in silico and in vivo approach to the development of PK, physiology based PK and PD models are proposed. Through a multiple PI plan, this application leverages the substantial experience of the individual PI's NIH funded research programs involving clinical biospecimen collection following loop diuretic administration and in vitro and in vivo experiments and modeling approaches of Dr. Testani and Dr. Prasad respectively.